The weakness of bone structure is a well-known condition to all surgeons in the orthopaedic field, in particular in the maxillo-facial and dental field. The causes are of several kinds, but quite well-known and understood. As regards means available to improve and reinforce the bones, it can be stated, that a wide variety of solutions have been proposed. Indeed, a number of techniques are currently available in the state of the art, which might be briefly distinguished in the following types: a) injections into target bone or cements or other mixtures; b) reinforcement with artificial supports to be added aside bone, being said supports metallic or polymeric o ceramic; c) tissue engineering, an approach wherein grafts are used that are made of osteoconductive and osteoinductive materials, such as e.g., some bioglasses; d) regenerative medicine, where artificial matrixes are used in order to host and deliver living cells to target area and thus enhance the formation of new resistant bone.
The introduction of new implant materials has allowed a remarkable development in bone reparative and reconstructive surgery in the last decades. Choosing an implant material is based on the osteogenesis, osteoinduction and osteoconduction properties of the material thereof. The most efficient solution among those currently available is to use an autologous bone as implant material, which implies, however, some disadvantages and risks. The quantity of material available to prepare the implant is limited and moreover the patient must undergo a dual intervention, the first for removing autologous bone and the second for the subsequent implant.
In accordance with the currently available techniques, an alternative way is represented by the usage of homologous tissue, that is the usage of demineralised bone matrix (DBM). The DBM is obtainable by a living donor or by a donor corpse. The human cortical derived DBM, however, has the same drawback of the autologous bone, i.e. the quantity of available material appears to be reduced. Further risks exist connected to possible infections, in particular viral and to potential compatibility problems, since the material to be implanted is of a heterologous nature. Moreover, the psychological aspect for the recipient, above all when the material is corpse-derived, represents an unnegligible critical element.
As it is known in the state of the art, as an alternative, the DBM may be of animal origin, in particular bovine. In the latter case, however, a microscopic examination can show that the bovine DBM porosity is higher than the cortical-derived human DBM, with a resulting minor compatibility and a reduced predisposition to the cell rooting and the growth of new integrated functional tissue.
The Applicant has observed that the higher porosity and the chemical structure of the bovine DBM result into a lower mechanical resistance, with a consequent higher weakness thereof. Such a weakness is particularly disadvantageous both in the pre-implant step, since shaping the matrix, according to the shape of the bone cavity which will host the matrix itself, with the desired accuracy is not easy, and in the implant in situ positioning step, because of the poor toughness of the matrix itself, which is often subject to a fragile fracture during the clamping steps.
Moreover, just because of the material weakness, the positioning and insertion of clamping elements (for example, screws) in such a matrix, is difficult and not enough accurate and, as stated before, it often causes the matrix break. Even further, during the shaping step of the matrix currently available in the state of the art, such as, for example, demineralised bone matrixes, bioglasses, bio-ceramics, etc., disadvantageously, undesirable powders are formed. For example, in dentistry, the shaping step takes place just before the implantation and the resulting powders creep up also on the matrix to be implanted.
Another proposed solution is a composite osteoimplant described in U.S. Patent Publication No. 2008/0063684. Such an osteoimplant includes a polymer and bone-derived particles. The composite is adapted and constructed to be formable during or immediately prior to implantation and to be set after final surgical placement.
U.S. Pat. No. 7,270,813 describes a method for preparing bone-derived composites, wherein the mineral portion of the bone is treated with a coupling agent before being incorporated into a biocompatible polymeric matrix. The resulting composite may be used as such that or be further processed to form an osteoimplant.
Therefore, there is the need in the field of regenerative bone surgery to find new bone implant matrixes, which have satisfactory characteristics of mechanical resistance and ductility to tri-dimensional processing.